This invention relates to the field of agricultural machinery and, more particularly, to improvements in seed planting machines.
Prior co-pending application Ser. No. 09/475,866 filed Dec. 30, 1999 and titled xe2x80x9cSeeding Machine with Bulk Seed Supply Container and Independent, Opener-Mounted Metering Devicesxe2x80x9d assigned to the assignee of the present invention (now U.S. Pat. No. 6,308,645) discloses a machine in which each opener is provided with its own seed metering device mounted directly on the opener for support. Rather than each individual metering device having its own separate seed box, groupings of the devices are supplied with seed from a common overhead seed container. Each metering device has its own metering wheel that takes power from a common transverse drive shaft on the main frame of the machine, there being individual chain and sprocket assemblies leading from the common drive shaft back to the metering wheels of the meters. Rotation of the metering wheels causes the singulation and metered dispensing of seeds down to the ground as the machine advances.
Each opener is independently mounted on the main frame for up and down swinging movement as the opener encounters rises and falls in the terrain relative to the main frame. While such responsiveness is desirable, the location of the drive shaft at a distance from the axes of swinging movement of the openers causes a slight momentary change in the length of the tight side of the drive chain of each opener during relative movement of the opener. This is due to the fact that, as the opener swings up and down, it also moves slightly fore-and-aft, changing the center-to-center distance between the axis of the drive shaft and the axis of the driven shaft of the metering wheel. This slight change momentarily retards or advances the metering wheel, depending upon whether the opener is moving toward or away from its median operating position. Such speed change has the effect of slightly varying the rate at which the metering wheel drops its seeds, causing undesirable variations in the seed spacing in the furrow. In the prior arrangement, the metering wheel rotates relatively slowly and has a large number of seed pockets about its periphery. Thus, even a slight change in the angular velocity of the metering wheel can have a significant effect upon seed spacing.
The present invention provides a way of keeping the tight, driving stretch of the chain substantially the same length throughout all positions of the opener in spite of the fact that the center-to-center distance between the drive shaft on the main frame and the driven sprocket on the meter changes as the opener responds to variations in ground contour. Guides, preferably in the form of smooth, free-wheeling rollers, are engaged with the tight stretch at such locations that the critical portion spanning the frame and the opener swings about an axis located to cause no lengthening or shortening of the spanning portion as it moves with the opener. In one embodiment, wherein the opener is supported on the main frame through a parallel linkage, the guides are so located that the spanning portion of the tight stretch remains substantially parallel to the upper and lower links of the parallel linkage, while the remaining opposite end portions of the tight stretch, being located on the main frame and the opener respectively, undergo no swinging movement at all. One guide is disposed on the nonmoving main frame, while a second guide is disposed on the opener.
In another preferred embodiment where the opener has only a single pivot point connection with the main frame, rather than a parallel linkage, a single guide is used in close proximity to the pivot point. This causes the spanning portion of the tight stretch leading from the guide to the metering wheel to essentially swing about the same pivot point as the opener itself, maintaining the spanning portion at a constant length over the full range of relative movement of the opener.